This invention relates to a method of making a cushion body of polyurethane and other synthetic resins.
Such cushion bodies have been widely used as, for instance, seat cushions and decorative panels applied to the interior of an automobile.
FIGS. 1 to 4 show prior art examples of synthetic resin cushion bodies. Particularly FIG. 1 shows, in section, a synthetic resin cushion body as comprising a surface layer 1 of, for instance, artificial leather and a filler pad of foamed polyurethane 2. As shown, the surface layer and the underlying filler pad are welded together at discrete positions 2a (five positions in this particular example). A filler pad may be of thin-skinned polyurethane or skinless polyurethane. The former is a polyurethane coated with a mold separating agent, which is ordinarily used in foaming the material, whereas the latter is a polyurethane molded at a relatively low temperature, thus causing no skin coating.
FIG. 2 shows the manner in which the surface layer 1 and the filler pad 2 are locally welded together. Specifically, the surface layer 1 is laid on the filler pad 2, and the two-layer body is sandwiched between two opposite plates 13 and 14 for dielectric heating. As shown, the upper dielectric heating plate 13 has a plurality of projections of same width "t" but different heights, whereas the lower dielectric heating plate 14 has no projections. (FIG. 2 shows the dielectric heating plates and the lamination sandwiched therebetween in the upside-down relation with their actual position in dielectric heating.) In dielectric heating, the two-layer body is compressed between the upper and lower plates, and then the elastic body yieldingly allows the projections of the lower plate 13 to invade the elastic body. An electric field of high frequency is applied across the thickness of the dielectric body to generate heat at discrete welding portions 2a, thereby melting the foamed material in the selected channels each "t" width. Then, the portions of the elastic body adjacent to the selected channels tend to return to their original stress-free shape, thus separating the foamed material from the opposite sides (shearing sides) 2b of each weld channel. Thus, the two-layer body when removed from the dielectric heating plates, is often found to be cut along each weld channel. Therefore, the dielectric heating is not appropriate for the purpose of welding a surface layer to an underlying filler pad.
In an attempt to avoid such shearing effect in the filler pad it has been proposed that a filler pad 2 is impregnated with a welding agent in selected channels across the thickness of the filler pad. The welding agent has a melting point below the melting temperature of polyurethane. A surface layer 1 is laid on the upper surface of the so-impregnated filler pad 2, and a backing layer 3 is laid on the lower surface of the filler pad. Then, the three-layer body is subjected to dielectric heating so that the filler pad 2 is welded under heat both to the overlying and underlying layers at the selected welding portions 2a of the filler pad, as shown in FIG. 3. In this case the filler pad 2 is compressed at discrete welding portions 2a in opposite directions. Thus, the resultant thickness "h" of the three-layer body is decreased as compared with the thickness "H" of the two-layer body of FIG. 1. Accordingly the cushion body is stiff somewhat, losing a pleasing voluminous appearance. Still disadvantageously, the production cost increases because of extra step of impregnation.
FIG. 4 shows a two-layer body as comprising a surface layer 1 and a filler pad 2 welded to the surface layer 1 at discrete portions 2a. This cushion body has no backing layer 3, and therefore the surface layer 1 cannot be corrugated or pleated as deeply as in the cushion body of FIG. 3. This is not appropriate for the purpose of giving a pleasing appearance to the surface of the cushion body. Disadvantageously the thin skin of the filler pad 2 welded under heat or glued to the surface layer 1, is liable to peel off from the filler pad, thus separating the surface layer from the filler pad. Fixing a filler pad to an overlying surface layer with the aid of a welding agent impregnated or otherwise applied to the filler pad or with the aid of a glue applied to the filler pad or to the surface layer disadvantageously increases the number of production steps, and hence the cost of production. Still disadvantageously, the resultant cushion body has a less pleasing appearance.